Answer:
Natural/Counting Numbers
Step-by-step explanation:
It is the smallest subset a number can classify into. It is all of the numbers from 1 to positive infinity.
9. 31 + 5 = 36
10. 16 - 4 = 12
12. 9
13. 44 + 34 = 78
14. 101 - 1 = 100
15. -539 ???
16. 15 ??
17. |-435| = 435
It's not possible nothing but 1 times 5 is the only thing that multiplies to 5 and 1+5 doesn't equal 4